The present invention relates, in general, to an improved apparatus for humidifying air and other gases, and more particularly to a humidifier system for breathing gases including means for directing the flow of gas through a water chamber, an alarm system for sensing the water level in the chamber, and means for sensing and controlling the temperature of the water, whereby warm, moist breathing gases may be supplied to a patient.
In the use of positive pressure respirators in the treatment of patients, it is frequently necessary to deliver breathing gas directly into the patient's trachea by an endotracheal tube or tracheostomy tube, thereby bypassing the patient's normal physiological humidifying and temperature regulating mechanisms. It is now well known that when this is done, it is necessary to deliver a breathing gas that has been warmed and humidified in order to avoid not only patient discomfort but the very real problem of seriously injuring the lungs of the patient. To this end, numerous devices have been developed in the prior art to treat the air prior to delivery to the patient, but these have not been entirely satisfactory, since in general they do not provide adequate control of the delivered air. For example, many commercially available humidifiers fail to provide a sensor or an alarm system to indicate when the humidifier is low on water, do not provide accurate control of the temperature of the breathing gas, and do not provide any means for protecting the humidifier from contamination by condensate or other foreign matter that may return to the humidifer by way of the outlet.
One of the more common systems available in the prior art for supplying humidified gas to a patient involves the use of an atomizer or nebulizer that mechanically separates the water into tiny liquid droplets which are injected into and combine with the flow of delivered gas. Such a system, however, presents serious problems since it is very difficult to control the temperature of the humidified gas that is delivered to the patient. Further, the system does not provide means for compensating for changes in the flowrate of the breathing gas, and does not provide any means for automatically sensing and indicating the need for additional water, so that it is possible for the system to become inoperative as a humidifier without providing any warning to the operator. Finally, the system has no means for protecting the humidifier from contamination via the outlet.
Another common humidifier system causes the breathing gas to be directed through a volume of heated water prior to reaching the patient and thus avoids the problems inherent in the nebulizer approach, but has not been found satisfactory since it provides a relatively low level of moisture in the outlet gas. Furthermore, the system has no provision for automatically sensing and indicating when the unit is low on water, and provides no protection against contamination through the outlet.
An improved version of the foregoing approach has been developed in which a diffusing or bubbling plate containing numerous small holes is placed in the path of the air flow. The breathing gas is delivered into a volume of water below the bubble plate and passes upwardly through the plate. The air flow is broken into small bubbles to increase the surface area of gas exposed to the water located above the plate, prior to delivery of the gas to the patient. Although this method increases the amount of moisture in the air, such systems in the prior art have not been entirely satisfactory since it has been found to be difficult to control the temperature of the humidified gas delivered to the patient because the diffusing plate causes an air barrier to form which varies in thickness between breaths. Such prior art systems also have made no provision for automatically sensing and indicating the need for additional water, and have provided no protection against the possibility of contaminants entering the humidifier through the breathing gas outlet.
Because such prior art systems provide inadequate control of the breathing gas temperature and moisture content, they have not been considered to be entirely reliable from the standpoint of patient safety and comfort, and accordingly have been unsatisfactory. In addition, the improvement of water and gas contact in the humidifier and improvement in the flow path to the patient in an attempt to provide greater stability and control in moisture content and gas temperature leads, in some cases, to an increased possibility of contamination of the water supply by bacteria from the patient. It has been found, for example, that when the warm moist air from the humidifier is delivered to the patient through a breathing tube, the air will cool and condensate will form on the inner surface. Condensate formed near the patient may pick up bacteria from the patient's respiratory tract, and any return flow of the condensate to the humidifier may carry such bacteria to the humidifier water supply, where it can proliferate and thus contaminate the supply.
Many of the attempts to meet these problems have resulted in complex, expensive humidifier systems which have been difficult to manufacture, hard to maintain in good working order, have required constant attention, and have thus generally been unsatisfactory.